basic embryology part i

Basic EmbryologyBasic Embryology

PART I

BASIC BASIC EMBRYOLOGYEMBRYOLOGY PART IPART I

EmbryologyEmbryology Embryology – study of the origin and

development of single individual Prenatal period

Embryonic period – first 8 weeks (56 days) Fetal period – remaining 30 weeks (210 days)

Copyright © 2008 Pearson Education, Inc., publishing as

Benjamin Cummings

Development of embryologyDevelopment of embryology Aristotle, B.C 384-322

Semen+menstration Harvey, 1651:

All life from oocyte Malpighi, 1675:

A micro-chicken in an egg Leewenhoek, 1677 :

A micro-human in a sperm

Haeckel, 1868

Biogenetic law

Spemann, 1869-1941 Experimental embryology

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as Benjamin Cummings

Embryonic Period


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Figure 3.1 (1 of 2)

Fetal Period


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Figure 3.1 (2 of 2)

The Basic Body PlanThe Basic Body Plan Skin – dermis and epidermis Outer body wall – trunk muscles, ribs, vertebrae Body cavity and digestive tube (inner tube) Kidneys and gonads – deep to body wall Limbs


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The Basic Body Plan


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Figure 3.2

The Embryonic PeriodThe Embryonic Period Week 1 – from zygote to blastocyst

Conception – in lateral third of uterine tube Zygote (fertilized oocyte) moves toward the uterus Blastomeres – daughter cells formed from zygote

Morula – solid cluster of 12–16 blastomeres “Mulberry”

Blastocyst – fluid-filled structure – ~ 60 cells


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The Embryonic PeriodThe Embryonic Period Stages of first week

Zygote 4-cell Morula Early blastocyst Late blastocyst (implants at this stage)


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Fertilization & Its processFertilization & Its process



nucleus acrosome

Penetration and release of acrosomal enzyme

Cell membrane of ovum

Sperm bind to sperm receptor ZP-3 induceAcrosome reaction ： release of acrosomal enzyme



ovum

spermfertilized ovum



Zona reaction: Cortical granules→perivitelline space →degrade ZP-3, alteration of zona pellucida →barrier for sperm penetration

The second meiotic division of the secondary oocyte is rapidly lifted and the second polar body is released, leaving a haploid female nucleus.

Contac of sperm and ovumContac of sperm and ovum



Sperm penetrate into the ovumSperm penetrate into the ovum



Formation & Fusion of Male and Formation & Fusion of Male and Female PronucleiFemale Pronuclei



Fertilization and the Events of the Fertilization and the Events of the First 6 Days of DevelopmentFirst 6 Days of Development


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Figure 3.3

Process of fertilization Process of fertilization



① Fusion of the membrane of

sperm and ovum

② The nucleus of sperm penetrate into ovum

③ Formation of pronuclei

④ Fusion of

pronuclei

Alteration of ovum

Week 2 – The Two-Layered Week 2 – The Two-Layered EmbryoEmbryo Bilaminar embryonic disc – inner cell mass

divided into two sheets Epiblast and the hypoblast

Together they make up the bilaminar embryonic disc


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Week 2 – The Two-Layered Week 2 – The Two-Layered EmbryoEmbryo Amniotic sac – formed by an extension of epiblast

Outer membrane forms the amnion Inner membrane forms the amniotic sac cavity

Filled with amniotic fluid


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Week 2 – The Two-Layered Week 2 – The Two-Layered EmbryoEmbryo Yolk sac – formed by an extension of hypoblast

Digestive tube forms from yolk sac NOT a major source of nutrients for embryo Tissues around yolk sac

Gives rise to earliest blood cells and blood vessels


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Implantation of the BlastocystImplantation of the Blastocyst


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Figure 3.4 (1 of 3)

Implantation of the Blastocyst…Implantation of the Blastocyst…


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Figure 3.4 (2 of 3)

Implantation of the Blastocyst…Implantation of the Blastocyst…


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Figure 3.4 (3 of 3)

Week 3 – The Three-Layered Week 3 – The Three-Layered Embryo…Embryo… Primitive streak – raised groove on the dorsal

surface of the epiblast Gastrulation – a process of invagination of

epiblast cells Begins at the primitive streak Forms the three primary germ layers


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Week 3 – The Three-Layered Week 3 – The Three-Layered Embryo…Embryo… Three Germ Layers*

Endoderm – formed from migrating cells that replace the hypoblast

Mesoderm – formed between epiblast and endoderm Ectoderm – formed from epiblast cells that stay on

dorsal surface

*All layers derive from epiblast cells!


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The Primitive StreakThe Primitive StreakCopyright © 2008 Pearson

Education, Inc., publishing as Benjamin Cummings

Figure 3.5e–h

The NotochordThe Notochord Primitive node – a swelling at one end of

primitive streak Notochord forms from primitive node and

endoderm Notochord – defines body axis

Is the site of the future vertebral column Appears on day 16


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Formation of the Mesoderm and NotochordFormation of the Mesoderm and NotochordCopyright © 2008 Pearson

Education, Inc., publishing as Benjamin Cummings

Figure 3.6

NeurulationNeurulation Neurulation – ectoderm starts forming brain and

spinal cord Neural plate – ectoderm in the dorsal midline

thickens Neural groove – ectoderm folds inward


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NeurulationNeurulationNeurulation (continued)

Neural tube – a hollow tube pinches off into the bodyCranial part of the neural tube becomes the

brainMaternal folic acid deficiency causes neural

tube defects


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NeurulationNeurulation Neural crest

Cells originate from ectodermal cells Forms sensory nerve cells

Induction Ability of one group of cells to influence

developmental direction of other cells


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The Mesoderm Begins to The Mesoderm Begins to DifferentiateDifferentiate Somites – our first body segments

Paraxial mesoderm Intermediate mesoderm – begins as a continuous

strip of tissue just lateral to the paraxial mesoderm


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Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Lateral plate – most lateral part of the mesoderm Coelom – becomes serous body cavities

Somatic mesoderm – apposed to the ectoderm Splanchnic mesoderm – apposed to the endoderm

The Mesoderm Begins to The Mesoderm Begins to DifferentiateDifferentiate

Basic EmbryologyBasic Embryology

PART II & IIIWILL BE COMING SHORTLYBY NEXT LECTURE IN SHAA ALLAH.

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LECTURE

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